[1] Procter & Gamble Pharmaceut, Staines, England
[2] Univ Utrecht, Dept Pharmacoepidemiol & Pharmacotherapy, Utrecht, Netherlands
[3] Sir Mortimer B Davis Jewish Hosp, Ctr Clin Epidemiol & Community Studies, Montreal, PQ H3T 1E2, Canada
[4] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ, Canada
[5] Univ Southampton, Southampton Gen Hosp, MRC, Environm Epidemiol Unit, Southampton, Hants, England